Hydrodynamic and Mass-Transfer Parameters of Gases in NICE F-T Wax Using a Pilot-Scale Slurry Bubble Column Reactor

摘要

The hydrodynamic and mass transfer parameters (gas holdup, ε_G, Sauter-mean diameter of gas bubbles,rndS, and volumetric liquid-side mass transfer coefficient, k_La) were measured for N_2 and N_2/He gaseousrnmixtures in a molten Fisher-Tropsch (F-T) wax produced by the National Institute of Clean-and-lowcarbonrnEnergy (NICE), China. The data were obtained in a pilot-scale (0.29 m) slurry bubble columnrnreactor (SBCR) operating under different pressures (4-31 bar), temperatures (380-500 K), and superficialrngas velocities (0.1-0.3 m/s) in the absence and presence of solid (iron-based catalyst) concentrations (0-rn15 vol.%). The effects of different operating variables on the hydrodynamic and mass transferrnparameters were investigated and the results were essentially compared with those previouslyrnpublished in a light F-T cut and in other F-T liquids.rnThe data obtained in NICE F-T wax showed that increasing reactor pressure increased ε_G and decreasedrnd_S which led to high values of k_La; while increasing temperature increased ε_G and k_La and decreased d_Srndue to the decrease of the liquid-phase viscosity and surface tension. Increasing the superficial gasrnvelocity increased ε_G and k_La, while d_S values remained essentially unaffected. Increasing catalystrnconcentration, however, decreased ε_G and k_La, and increased d_S. Also, under similar operatingrnconditions, ε_G, gas-liquid interfacial area (a) and k_La of N_2 or N_2-rich gaseous mixtures were greater thanrnthose of He or He-rich mixtures due to the former’s greater density and momentum, which led to thernformation of smaller d_S and greater ε_G.rnUnder high temperatures, the gas-liquid interfacial areas were greater, whereas the k_La values werernsmaller in NICE F-T wax when compared with those reported in the light F-T cut. This behavior wasrnattributed to the smaller mass transfer coefficients (Kl) of NICE F-T wax due its higher viscosity whenrncompared with that of the light F-T cut.